Within the aspects connected to good brushing, as studied by dentists and toothbrush manufacturers, one of the most important ones has been the optimization of the bristle pressure applied to the teeth and gums, so as to provide maximum bucal hygiene, without loss or lesion to the gums or to the dentine or enamel of the teeth.
Just as there are more easily accessible regions in the dental arcades, where brushing is more comfortable and the force applied to the brush can be more easily controlled, there are other regions of more difficult access, frequently requiring the user to change the position of his or her hand, and where it is found that the user loses control over the force applied to the brush.
The result is that bucal hygienic using conventional toothbrushes leads to uneven brushing, causing gum and bucal deterioration in some regions due both to deficient cleaning and excessive abrasion by brushing.
In order to overcome the foregoing problem, it has become clear that a toothbrush should be provided with some means to absorb part of the force applied by the user to the toothbrush.
In addition to variations in the flexibility of the bristles, the adopted solutions generally consist of applying a resiliently flexible means to a region of the brush head or, more frequently, to an intermediate portion between the brush handle and head.
Among the solutions directed to the head construction is one described in PCT/EP/92/00645 (WO92/17092) which describes a toothbrush provided with a flexible head, resiliently connected to a prolonged portion of the handle, the latter surrounding the brush head or the head partially surrounding the prolonged portion, the head being cable of making an oscillatory movement in relation to the prolonged portion of the handle. In a second solution, described in U.S. Pat. No. 4,633,542, a soft elastomer is applied under the bristles. In a third solution, described in U.S. Pat. No. 2,631,320, the brush head is cut between each transverse row of bristles, the different portions thus formed being spacedly interconnected by a longitudinal laminate spring element, fixed at one end to the brush handle, in such a way as to become vertically bendable.
Such solutions, among others applied to the toothbrush head, have two limitations in common which, by themselves, tend to render such brushes commercially unfeasible: high cost, due to their complex construction, and the impossibility of adequate cleaning of the brush after use, whereby the head cumulatively retains food residues and thus propitiates the proliferation of fungus, bacteria and other microorganisms.
Consequently, since they avoid the above serious limitations, many resiliently flexible brushes incorporate their resilient deflecting means in an intermediate portion between the brush handle and head.
One manner which has proved to be efficient to obtain a resiliently flexible means for controlled articulation of the head of a toothbrush with its handle, at an accessible cost for the consumer, was by weakening the intermediate portion between the handle and the head, that is, the toothbrush neck, by removing the material comprising the handle, such as described in patent DE 36,40898.
Within such principle of construction, many other more complex solutions have been presented: in a first solution, described in PCT/EP93/00299 (WO93/15627), the neck is provided with many annular grooves, in such a manner as to form a single central beam with a reduced diameter and incorporating a plurality of flanges with a profile substantially the same as that of the handle. In this construction, the degree of neck flexibility is determined by the diameter and the extension of the central beam that defines the neck and the angular limit of head displacement in relation to the handle is determined by the abutment of flanges against each other.
In a second construction, described in U.S. Pat. No. 4,520,526, the brush is provided with a resiliently flexible neck obtained by removal of the material from the front and back faces of the handle, to form corresponding cavities so as to produce an area of reduced cross section. In a third solution, also described in U.S. Pat. No. 4,520,526 as well as PCT/US92/00681 (WO92/15225), material is removed from the intermediate portion of the brush neck, so as to define a longitudinally extended transverse through aperture that is limited by front and rear longitudinal beams, the greater or lesser thickness of such beams determining a greater or lesser resistance to bending of the brush head in relation to the handle, in an axial plane which is parallel to the axis of the bristles.
Other variations of the construction described in the last example have also been developed, such as the one described in U.S. Pat. No. 5,146,645, in which a reduction of the thickness is provided in a median region of the front beam, defining a point of lower mechanical or of localized bending so as to allow such median region of the beam to bend, as a result of a force applied by the user to the brush, until it abuts the front face of the rear beam, indicating to the user that he/she has exceeded the acceptable limit of brushing force.
In spite of solving, to a greater or lesser degree, the basic problems related to complexity and hygienics as previously mentioned, the foregoing constructions suffer from two new drawbacks, namely: upon bending the brush, and considering that the user always tends to keep the brush handle in the same position when brushing a given tooth, the angle of contact of the bristles in relation to the tooth is altered by a value substantially equal to the angle formed between the bent brush head and the handle, resulting in deficient brushing and uneven wear of the bristles. In addition, as these toothbrushes are generally molded as a single piece made of thermoplastic material, constant localized bending of one of the neck beams causes fatigue and weakening of the material at the point of the bending, reducing its elastic memory, which causes a cumulative deformation of the toothbrush, which generally becomes useless due to the excessive deformation of its neck when its bristles are still in good condition.
Yet, within the construction which provides for a flexible neck, another solution is suggested, as described in U.S. Pat. No. 5,315,732, according to which the neck is defined by a pair of front and rear flexible laminate beams, such beams having their bending extension controlled by a piston which slides between the beams and incorporated to an end of a rigid rod, the other end of which is manually, but relatively tightly slidable, in an axial groove in the brush body. The piston positioning adjusts the length of the beams that is a available for bending and, consequently, the degree to which the neck is flexible. It happens that, apart from involving a complex construction, this solution requires from the user a certain practice and some care in order to obtain an adjustment that meets his/her brush use characteristics. This construction has the positive aspect of adjusting the degree of neck flexibility which however, is annulled by the impossibility of keeping the same dihedral angle between the handle and the head upon moving the latter and by the fact that this kind of construction tends to result in the accumulation of residues.
It is, therefore, the overall object of this invention to provide a toothbrush which is resiliently flexible between its head and handle, of low cost, high brushing performance, of long life, and easy to clean.
It is a specific object of this invention to provide a toothbrush, as above described, which may keep the working plane of the bristles at a substantially constant angle with respect to the longitudinal axis of the handle, even under maximum contact pressure of the bristles.
It is also an object of this invention to provide a toothbrush, as above described, the neck of which has a substantially constant elastic memory throughout the useful life of its bristles.
It is further an object of this invention to provide a toothbrush, as described above, which allows the manufacturer or the user to vary the degree of flexibility of the brush neck, without changing the construction of its body, head or neck.
These and other objectives and advantages of the present invention are obtained by providing a toothbrush comprising: an elongated handle; a head with a front face, in which a set of bristles is affixed; and a flexible neck, interlinking the handle and the head. In accordance with the invention, the neck is defined by a front longitudinal beam and a rear longitudinal beam that are spaced from each other and have their opposite ends respectively connected to the head and handle though localized bending regions, whereby the head may be slid, both transversally and relative to the handle, in a plane containing the longitudinal axis of the handle and which is parallel to the bristles axes, from an inoperative rest position to operative positions, by maintaining the same dihedral angle between the longitudinal axes of the handle and head, such brush being also provided with an elastic shock absorbing means acting in the neck, in such a manner as to be elastically deformed when the head is displaced from its inoperative position to any of its operative positions, such elastic shock absorbing means constantly biasing the head towards its inoperative position. In practical terms, the toothbrush according to the invention combines the known advantages of the conventional brush and of a resiliently flexible brush, that is, low cost, constant positioning of the working plane of the bristles against gums and teeth and suitable adjustment of brushing pressure.
In addition, besides not presenting any of the usual limitations of the known toothbrushes, the proposed brush also presents two other entirely new aspects, by way of a manner for maintaining the elastic memory which, when applied to the brush neck, means that its elastic memory is extended to the whole useful life of the bristles, and the adjustment of the degree of neck flexibility, without changing the basic features of the brush, by using different shock absorbing means, selected in accordance with the user's particular needs.